It is synthesized by Micromonospora, a genus of Gram-positive bacteria widely present in the environment (water and soil). To highlight their specific biological origins, gentamicin and other related antibiotics produced by this genus (verdamicin, mutamicin, sisomicin, netilmicin, retymicin) generally have their spellings ending in ~micin and not in ~mycin. Gentamicin is a bactericidal antibiotic that works by binding the 30S subunit of the bacterial ribosome, interrupting protein synthesis.

Like all aminoglycosides, when gentamicin is given orally, it is not systemically active. This is because it is not absorbed to any appreciable extent from the small intestine. It is administered intravenously, intramuscularly or topically to treat infections. It appears to be completely eliminated unchanged in the urine. Urine must be collected for many days to recover all of a given dose because the drug binds avidly to certain tissues.

E. coli has shown some resistance to gentamicin, despite being Gram-negative. Reluctance to use gentamicin for empirical therapy has led to increased use of alternative broad-spectrum antibiotics, which some experts suggest has led to the prevalence of antibiotic-resistant bacterial infections by Golden Staph and other so-called "superbugs".[1]

Gentamicin is one of the few heat-stable antibiotics that remain active even after autoclaving, which makes it particularly useful in the preparation of some microbiological growth media. It is used during orthopaedic surgery when high temperatures are required for the setting of cements (e.g. hip replacements).[2]

Side effects

These aminoglycosides are toxic to the sensory cells of the ear, but they vary greatly in their relative effects on hearing versus balance. Gentamicin is a vestibulotoxin, and can cause permanent loss of equilibrioception, caused by damage to the vestibular apparatus of the inner ear, usually if taken at high doses or for prolonged periods of time, but there are well documented cases in which gentamicin completely destroyed the vestibular apparatus after three to five days.[citation needed] A small number of affected individuals have a normally harmless mutation in their mitochondrial RNA (m1555 A>G), that allows the gentamicin to affect their cells. The cells of the ear are particularly sensitive to this, sometimes causing complete hearing loss.[4] However, gentamicin is sometimes used intentionally for this purpose in severe Ménière's disease, to disable the vestibular apparatus.

Gentamicin can also be highly nephrotoxic, particularly if multiple doses accumulate over a course of treatment. For this reason gentamicin is usually dosed by body weight. Various formulae exist for calculating gentamicin dosage. Also trough and peak serum levels of gentamicin are monitored during treatment, generally before and after the third dose is infused.

Side effects of gentamicin toxicity vary from patient to patient. Side effects may become apparent shortly after or up to months after gentamicin is administered. Symptoms of gentamicin toxicity include:

Psychiatric symptoms related to gentamicin can occur. These include anorexia, confusion, depression, disorientation and visual hallucinations.[6] Immediate professional help should be sought if any of these symptoms or others appear after administration of aminoglycosides. General medical practitioners should refer patients with such symptoms to an otolaryngologist, commonly known as an 'ear, nose, and throat doctor', for comprehensive tests.

A number of factors and determinants should be taken into account when using gentamicin, including differentiation between empirical and directed therapy which will affect dosage and treatment period.[1] Many medical practitioners freely administer gentamicin as an antibiotic without advising patients of the severe and permanent potential ramifications of its use. Gentamicin is well known to be a cheap, low cost yet old medicine as compared to modern alternatives, and is typically US$3–6 per dosage less than modern alternatives.

Many people recover from gentamicin toxicity naturally over time if the drug is discontinued, but they recover slowly and usually incompletely.[citation needed] Sometimes the toxicity of gentamicin can still increase over months after the last dose. Upon cessation of gentamicin therapy symptoms such as tinnitus and imbalance may become less pronounced. Sensori-neural hearing loss caused by gentamicin toxicity is permanent however.

Production and usage in research

Gentamicin is produced by a fermentation procedure. It was discovered by a Chinese microbiologist, Yue Wang. The majority of the world's gentamicin production takes place in China and South Korea; the last European producer is Lek, part of Sandoz group.

Gentamicin has been used since the early 1980s in microbiological research. The gentamicin protection assay enables researchers to quantify the ability of pathogenic bacteria to invade eukaryotic cells. It takes advantage of the fact that gentamicin is not able to penetrate eukaryotic cells.

gentamicin — A group of aminoglycoside antibiotics produced by Micromonospora spp. Members include the closely related gentamycins C1, C2 and C1a, together with gentamycin A. They inhibit protein synthesis on 70S ribosomes by binding to the 23S core protein… … Dictionary of molecular biology